Method and apparatus for providing uplink signal-to-noise ratio (SNR) estimation in a wireless communication

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

0001This application claims priority to U.S. Provisional Application No. 60/452,790 filed Mar. 6, 2003, entitled “Method and Apparatus for a Reverse Link Communication in a Communication System,” and assigned to the assignee hereof and hereby expressly incorporated by reference herein.

BACKGROUND

00021. Field

0003The present invention relates generally to communication systems, and, more specifically, to a method and apparatus for providing uplink signal-to-noise ratio (SNR) estimation in a wireless communication system.

00042. Background

0005Wireless communication technologies have seen explosive growth over the past few years. This growth has been primarily fueled by wireless services providing freedom of movement to the communicating public as opposed to being “tethered” to a hard-wired communication system. It has also been fueled by the increasing quality and speed of voice and data communications over the wireless medium, among other factors. As a result of these enhancements in the communications field, wireless communications has had, and will continue to have, a significant impact on a growing number of the communicating public.

0006One type of wireless communication system includes a Wideband Code Division Multiple Access (W-CDMA) system, which is configured to support both voice and data communications. This system may have multiple base transceiver sites that communicate over a wireless link with a plurality of mobile terminals. The base transceiver site transmits data and control information to the mobile terminal over a set of forward link channels and the mobile terminal transmits data and control information to the base transceiver site over a set of reverse link channels. In particular, the reverse link channels transmitted from the mobile terminal to the base transceiver site include a pilot channel, traffic channel, and rate indicator channel, among others. The traffic channel transmits data from the mobile terminal to the base transceiver site. The rate indicator channel provides a data rate to the base transceiver site indicating the rate at which data is being transmitted over the traffic channel. The pilot channel may be used by the base transceiver site for an amplitude and phase reference for demodulating the data on the traffic channel.

0007The reverse link channels are typically power controlled to compensate for variations in the received signals due to variations through the communication medium between the mobile terminal and base transceiver site. This power control process is usually based on measuring the signal-to-noise ratio (SNR) of the pilot channel. For example, the base transceiver site periodically measures the SNR of the pilot channel received from the mobile terminal and compares it to a target SNR. If the measured SNR is below the target SNR, the base transceiver site transmits to the mobile terminal an “UP” command. This directs the mobile terminal to increase the power level of the pilot channel, as well as the other channels. If the measured SNR is above the target SNR, the base transceiver site sends a “DOWN” command to the mobile terminal. This directs the mobile terminal to decrease the power level of the channels. The mobile terminal increases or decreases the transmit power of the channels by a fixed upward or downward step.

0008Typically, as the data rate on the traffic channel increases, the signal power of the traffic channel is also increased by the mobile terminal to accommodate the increased data rate. For an efficient operation of the communication link, the pilot power typically needs to be increased to provide better phase estimation for the higher data rates. However, because the maximum total signal power at which the mobile terminal may transmit over each of the reverse link channels is limited to a finite amount of power, the signal power level of the pilot channel is set to a nominal signal power level to enable an increase in the signal power level of the traffic channel to accommodate the increased data rate and minimize the pilot channel overhead. By keeping the signal power level of the pilot channel to a nominal signal power level, the estimation of the SNR of the pilot channel may not be as precise as if it were transmitted at a higher signal power level. As a result, the inner-loop power control of the wireless communication system may be adversely impacted due to the decreased reliability in the measured SNR of a lower signal power level transmitted on the pilot channel.

0009The present invention is directed to overcoming, or at least reducing the effects of, one or more problems indicated above.

SUMMARY

0010In one aspect of the invention, a method in a wireless communication system is provided. The method comprises receiving a first signal over a first channel and a second signal over a second channel, where the second signal is received at a higher signal power level than the first signal. A signal-to-noise ratio (SNR) of the second signal is measured, and the SNR of the first signal is determined based at least in part upon the measured SNR of the second signal.

0011In another aspect of the invention, an apparatus is provided. The apparatus comprises at least one transmitter for transmitting a first signal over a first channel and a second signal over a second channel, where the second signal is transmitted at a higher signal power level than the first signal. The system further comprises at least one receiver for receiving the first and second signals. The receiver measures a signal-to-noise ratio (SNR) of the second signal and determines the SNR of the first signal based at least in part upon the measured SNR of the second signal.

0012In another aspect of the invention, a device is provided. The device comprises a receiver for receiving a first signal over a first channel and a second signal over a second channel, where the second signal is received at a higher signal power level than the first signal. The receiver device further comprises a processor for measuring a signal-to-noise ratio (SNR) of the second signal and determining the SNR of the first signal based at least in part upon the measured SNR of the second signal.

0013In another aspect of the invention, a mobile terminal is provided. The mobile terminal comprises a transmitter that transmits a first signal over a first channel and a second signal over a second channel to a base transceiver site, where the second signal is transmitted at a higher signal power level than the first signal. The base transceiver site receives the first and second signals, measures a signal-to-noise ratio (SNR) of the second signal, and determines the SNR of the first signal based at least in part upon the measured SNR of the second signal.

0014In another aspect of the invention, a computer readable media embodying a method for a wireless communication system is provided. The method comprises receiving a first signal over a first channel and a second signal over a second channel, where the second signal is received at a higher signal power level than the first signal. A signal-to-noise ratio (SNR) of the second signal is measured, and the SNR of the first signal is determined based at least in part upon the measured SNR of the second signal.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram of a wireless communication system in accordance with one illustrative embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 2</figref> shows a more detailed representation of a mobile terminal that communicates in the wireless communication system of <figref idref="DRAWINGS">FIG. 1</figref>;

<figref idref="DRAWINGS">FIG. 3</figref> depicts a more detailed representation of a base transceiver site within the wireless communication system of <figref idref="DRAWINGS">FIG. 1</figref>;

<figref idref="DRAWINGS">FIG. 4</figref> is a diagram illustrating forward and reverse link channels used between the mobile terminal and the base transceiver site;

<figref idref="DRAWINGS">FIGS. 5A and 5B</figref> show the transmission of a rate indicator channel in a code division multiplex (CDM) and time division multiplex (TDM) manner, respectively;

<figref idref="DRAWINGS">FIG. 6</figref> illustrates a plot conveying the relative signal power levels at which a traffic channel, rate indicator channel, and pilot channel are transmitted by the mobile terminal to the base transceiver site;

<figref idref="DRAWINGS">FIG. 7</figref> shows a look-up table, which is stored at the base transceiver site, that provides a relationship between a data rate of the traffic channel, a traffic-to-pilot ratio, and a RICH-to-pilot ratio of the respective reverse link channels; and

<figref idref="DRAWINGS">FIG. 8</figref> is a flow diagram illustrating a method for providing an estimation of a pilot SNR and symbol SNR in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION

0023Turning now to the drawings, and specifically referring to <figref idref="DRAWINGS">FIG. 1</figref>, a wireless communication system <b>100</b> is shown in accordance with one embodiment of the present invention. The wireless communication system <b>100</b> comprises a plurality of mobile terminals (MT) <b>105</b> that communicate with a plurality of base transceiver sites (BTS) <b>110</b>, which are geographically dispersed to provide continuous communication coverage with the mobile terminals <b>105</b> as they traverse the wireless communication system <b>100</b>.

0024The mobile terminals <b>105</b> may, for example, take the form of wireless telephones, personal information managers (PIMs), personal digital assistants (PDAs), or other types of computer terminals that are configured for wireless communication. The base transceiver sites <b>110</b> transmit data to the mobile terminals <b>105</b> over a forward link of a wireless communication channel <b>115</b>, and the mobile terminals <b>105</b> transmit data to the base transceiver sites <b>110</b> over a reverse link of the channel <b>115</b>.

0025In one embodiment, the wireless communication system <b>100</b> conforms generally to a release of the W-CDMA (Wideband Code Division Multiple Access) specification. W-CDMA is a 3rd Generation (3G) wireless communication standard that is based on the IS-95 standard. In accordance with the illustrated embodiment, the wireless communication system <b>100</b> is intended to operate utilizing 3GPP (3^rdGeneration Partnership Project) Release 6 of the W-CDMA standard, but other embodiments may be implemented in other releases of the W-CDMA standard. In an alternative embodiment, the wireless communication system <b>100</b> may operate in accordance with 3GPP2 Revision D of the cdma2000 standard. It will be appreciated that the embodiments described herein should be considered as exemplary rather than limiting. Accordingly, the system <b>100</b> may take the form of various other types of wireless communication systems without departing from the spirit and scope of the present invention.

0026Each base-transceiver site <b>110</b> is coupled to a base station controller (BSC) <b>120</b>, which controls connections between the base transceiver sites <b>110</b> and other communication system components of the wireless communication system <b>100</b>. The base transceiver sites <b>110</b> and the base station controller <b>120</b> collectively form a radio access network (RAN) for transporting data to and from the plurality of mobile terminals <b>105</b> that communicate within the wireless communication system <b>100</b>. The base transceiver sites <b>110</b> are coupled to the base station controller <b>120</b> by communication links <b>125</b>, which may take the form of a wireline E1 or T1 link. The communication links <b>125</b>, however, may alternatively be embodied using any one of a number of wired or wireless communication mediums including, but not necessarily limited to, microwave, optical fiber, and the like. Additionally, the simplified depiction of the wireless communication system <b>100</b> in <figref idref="DRAWINGS">FIG. 1</figref> is merely for ease in conveying the present invention. It will be appreciated, however, that the wireless communication system <b>100</b> may be configured with any number of mobile terminals <b>105</b>, base transceiver sites <b>110</b>, and base station controllers <b>120</b> without departing from the spirit and scope of the present invention.

0027The base station controller <b>120</b> may be coupled to various communication system components to effectively extend the communication capabilities available to the mobile terminals <b>105</b> beyond the wireless communication system <b>100</b>. The communication system components may include a data server <b>140</b>, a public switched telephone network (PSTN) <b>150</b>, and the Internet <b>160</b> for access by the mobile terminals <b>105</b>. It will be appreciated that the communication system components illustrated in <figref idref="DRAWINGS">FIG. 1</figref> are for exemplary purposes only, and that the wireless communication system <b>100</b> may be interfaced with various other types of communication system components without departing from the spirit and scope of the present invention.

0028Turning now to <figref idref="DRAWINGS">FIG. 2</figref>, a more detailed representation of the mobile terminal <b>105</b> is shown in accordance with one embodiment of the present invention. In one of its simpler forms, the mobile terminal <b>105</b> comprises a transmitter <b>205</b> for transmitting data over the reverse link of the wireless communication channel <b>115</b> to the base transceiver sites <b>110</b>. The mobile terminal <b>105</b> also includes a receiver <b>210</b> for receiving data transmitted from the base transceiver sites <b>110</b> over the forward link of the wireless communication channel <b>115</b>. In an alternative embodiment, the transmitter <b>205</b> and receiver <b>210</b> may be combined into a single transceiver unit as opposed to being embodied as two separate entities as illustrated in the figure. The transmitter <b>205</b> and the receiver <b>210</b> are coupled to an antenna <b>215</b> to facilitate the wireless transmission and reception of data over the wireless communication channel <b>115</b>.

0029The mobile terminal <b>105</b> further comprises a processor <b>220</b> for controlling various operating functions and a memory <b>225</b> for storing data. In one embodiment, the processor <b>220</b> may take the form of a digital signal processor (DSP) chip. It will be appreciated, however, that the processor <b>220</b> may take the form of various other commercially-available processors or controllers.

0030The mobile terminal <b>105</b> also comprises a data input unit <b>230</b>, which provides data for transmission to the base transceiver sites <b>110</b> over the wireless communication channel <b>115</b>. The data input unit <b>230</b> may take the form of a microphone or an input from a data generating device, such as a computer terminal, for example. It will be appreciated that the data input unit <b>230</b> may be implemented in various other forms to provide data to the processor <b>220</b>, and, thus, need not necessarily be limited to the aforementioned examples.

0031The data received through the data input unit <b>230</b> is processed by the processor <b>220</b> and then forwarded to the transmitter <b>205</b> for transmission over the reverse link of the wireless communication channel <b>115</b> to the base transceiver sites <b>110</b>. Data received by the receiver <b>210</b> over the forward link of the wireless communication channel <b>115</b> from the base transceiver sites <b>110</b> is forwarded to the processor <b>220</b> for processing and then to data output unit <b>235</b> for various purposes, such as presentation to the user of the mobile terminal <b>105</b>, for example. The data output unit <b>235</b> may take the form of at least one of a speaker, visual display, and an output to a data device (e.g., a computer terminal), or any combination thereof. It will be appreciated that the data output unit <b>235</b> may comprise various other visual or aural perceptible devices, and, thus, need not necessarily be limited to the aforementioned examples. Furthermore, the simplified depiction of the mobile terminal <b>105</b> in <figref idref="DRAWINGS">FIG. 2</figref> is merely for ease in conveying the present invention. Accordingly, it will also be appreciated that the mobile terminal <b>105</b> may include other components to enable various other features and/or capabilities of the mobile terminal <b>105</b> than those illustrated.

0032Referring now to <figref idref="DRAWINGS">FIG. 3</figref>, a more detailed representation of the base transceiver site <b>110</b> is shown according to one embodiment of the present invention. In one of its simpler forms, the base transceiver site <b>110</b> comprises a transmitter <b>305</b> for transmitting data over the forward link of the wireless communication channel <b>115</b> to the mobile terminal <b>105</b>, and a receiver <b>310</b> for receiving data from the mobile terminals <b>105</b> over the reverse link of the wireless communication channel <b>115</b>. In an alternative embodiment, the transmitter <b>305</b> and receiver <b>310</b> may be combined into a single transceiver unit as opposed to being embodied as two separate entities as illustrated. The transmitter <b>305</b> and the receiver <b>310</b> are coupled to an antenna <b>315</b> to facilitate the transmission and reception of data over the wireless communication channel <b>115</b>.

0033The base transceiver site <b>110</b> is further configured with a processor <b>320</b> for controlling various operating features and a memory <b>325</b> for storing data. In one embodiment, the processor <b>320</b> may take the form of a digital signal processor (DSP) chip. It will be appreciated, however, that the processor <b>320</b> may take the form of various other commercially-available processors or controllers. The base transceiver site <b>110</b> further comprises a communication interface <b>340</b> for interfacing the base transceiver site <b>110</b> to the base station controller <b>120</b>. It will be appreciated that the base transceiver site <b>110</b> may be configured with additional components to perform a variety of other functions than those illustrated.

0034The wireless communication channel <b>115</b> includes various channels for communication between the base transceiver site <b>110</b> and the mobile terminal <b>105</b>. Referring to <figref idref="DRAWINGS">FIG. 4</figref>, a diagram illustrating the plurality of channels between the base transceiver site <b>110</b> and the mobile terminal <b>105</b> is shown. Base transceiver site <b>110</b> transmits data to mobile terminal <b>105</b> via a set of forward link channels <b>410</b>. These forward link channels <b>410</b> typically include data channels through which data is transmitted and control channels through which control signals are transmitted.

0035Mobile terminal <b>105</b> transmits data to the base transceiver site <b>110</b> via a set of reverse link channels <b>420</b>, which also include both data and control channels. In particular, the mobile terminal <b>105</b> transmits information to the base transceiver site <b>110</b> over a dedicated physical control channel (DPCCH) (e.g., a pilot channel) <b>422</b>, a dedicated physical data channel (R-DPDCH) (e.g., a traffic channel) <b>424</b>, and a rate indicator channel (R-RICH) <b>426</b>.

0036The information transmitted over these reverse link channels <b>420</b> from the mobile terminal <b>105</b> to the base transceiver site <b>110</b> is represented by bits. Several bits are grouped together into a frame and encoded into modulation symbols. The modulation symbols are then transmitted over the appropriate reverse link channels <b>420</b> to the base transceiver site <b>110</b>. For example, rate indicator bits are encoded into rate indicator modulation symbols and are then transmitted over the rate indicator channel R-RICH <b>426</b>. Similarly, bits of traffic data are encoded into data modulation symbols, and transmitted over the traffic channel R-DPDCH <b>424</b>.

0037The traffic channel R-DPDCH <b>424</b> carries a signal comprising frames of data from the mobile terminal <b>105</b> to the base transceiver site <b>110</b>. The data rate at which these frames are transmitted is typically variable. Usually, as the data rate over the traffic channel R-DPDCH <b>424</b> increases, the amount of power needed to transmit the data traffic signal over the traffic channel R-DPDCH <b>424</b> also increases.

0038The rate indicator channel R-RICH <b>426</b> carries a signal comprising rate indicator frames that correspond to the data traffic frames transmitted on the traffic channel R-DPDCH <b>424</b>. Each of the rate indicator frames identifies the data rate of the corresponding data traffic frame. The rate indicator channel R-RICH <b>426</b> further carries Hybrid Automatic Repeat Request (HARQ) information (such as sub-packet ID, redundancy version, etc.), which enables the base transceiver site <b>110</b> to decode the traffic channel R-DPDCH <b>424</b>. The HARQ bits enable the base transceiver site <b>110</b> to either soft-combine the received data symbols with previous transmissions over the traffic channel R-DPDCH <b>424</b> prior to decoding or to decode the received symbols independently. The rate indicator channel R-RICH <b>426</b> typically has a fixed, low data rate.

0039The pilot channel DPCCH <b>422</b> carries a pilot signal that provides an amplitude and phase reference, for example, for demodulating the data on the traffic channel R-DPDCH <b>424</b>. Accordingly, the pilot channel DPCCH <b>422</b> may be used as a demodulation reference by the base transceiver site <b>110</b> for demodulating received signals from the mobile terminal <b>105</b>. In accordance with the illustrated embodiment, the pilot signal has a fixed, low data rate to enable the mobile terminal <b>105</b> to transmit over the traffic channel R-DPDCH <b>424</b> at a higher signal power to accommodate higher data rates transmitted thereover.

0040In one embodiment, the rate indicator channel R-RICH <b>426</b> is transmitted in a code division multiplex (CDM) manner as illustrated in <figref idref="DRAWINGS">FIG. 5A</figref>, in which the rate indicator channel R-RICH <b>426</b> is transmitted on a separate code channel from the traffic channel R-DPDCH <b>424</b>. In an alternative embodiment, the rate indicator channel R-RICH <b>426</b> may be transmitted in a time division multiplex (TDM) manner with the traffic channel R-DPDCH <b>424</b> on the same code channel on a time division basis as illustrated in <figref idref="DRAWINGS">FIG. 5B</figref>.

0041Typically, as the data rate on the traffic channel R-DPDCH <b>424</b> increases, the signal power of the traffic channel R-DPDCH <b>424</b> is also increased by the mobile terminal <b>105</b> to accommodate the increased data rate. For an efficient operation of the communication link, the pilot power is typically increased to provide better phase estimation for higher data rates. Because the maximum total signal power at which the mobile terminal <b>105</b> may transmit over each of the reverse link channels <b>420</b> is limited to a finite amount of power, the signal power level of the pilot channel DPCCH <b>422</b> is set to a nominal signal power level to enable an increase in the signal power level of the traffic channel R-DPDCH <b>424</b> to accommodate the increased data rate and minimize the pilot channel DPCCH <b>422</b> overhead.

0042By keeping the signal power level of the pilot channel DPCCH <b>422</b> to a nominal signal power level, however, the estimation of the signal-to-noise ratio (SNR) of the pilot channel DPCCH <b>422</b> may not be as precise as if it were transmitted at a higher signal power level. By measuring the SNR of the rate indicator channel R-RICH <b>426</b>, which is transmitted at a higher signal power level than the pilot channel DPCCH <b>422</b>, a more accurate estimation of the pilot channel SNR may be determined. As a result of achieving a more accurate SNR of the pilot channel DPCCH <b>422</b>, the wireless communication system <b>100</b> may achieve a more efficient inner-loop power control and symbol scaling for turbo decoding.

0043Turning now to <figref idref="DRAWINGS">FIG. 6</figref>, a plot illustrating the relative signal power levels at which the traffic channel R-DPDCH <b>424</b>, rate indicator channel R-RICH <b>426</b>, and pilot channel DPCCH <b>422</b> are transmitted by the mobile terminal <b>105</b> to the base transceiver site <b>110</b> is shown for a particular data rate. In accordance with the illustrated embodiment, the signal power level of the pilot channel DPCCH <b>422</b> is kept to a nominal level to permit the traffic channel R-DPDCH <b>424</b> to be transmitted at a higher signal power level to accommodate a higher data rate. In the illustrated embodiment, the traffic-to-pilot (T/P) ratio (i.e., the energy-per-chip ratio of the data signal on the traffic channel R-DPDCH <b>424</b> to the pilot signal on the pilot channel DPCCH <b>422</b>) is kept relatively high as compared to the RICH-to-pilot (R/P) ratio (i.e., the energy-per-chip ratio of the rate indicator signal on the rate indicator channel R-RICH <b>426</b> to the pilot signal on the pilot channel DPCCH <b>422</b>). As the data rate increases over the traffic channel R-DPDCH <b>424</b>, the difference between the traffic-to-pilot and RICH-to-pilot ratios also increases. The relationship between the traffic-to-pilot and RICH-to-pilot ratios plays a significant role in determining the SNR of the pilot channel DPCCH <b>422</b> and the traffic channel R-DPDCH <b>424</b>.

0044Referring now to <figref idref="DRAWINGS">FIG. 7</figref>, a look-up table <b>700</b> providing a relationship between a data rate <b>710</b> of the traffic channel R-DPDCH <b>424</b> and a desired traffic-to-pilot ratio <b>720</b> and RICH-to-pilot ratio <b>730</b> is shown according to one embodiment of the present invention. In accordance with one embodiment, the table <b>700</b> is stored within the memory <b>325</b> of the base transceiver site <b>110</b>, and provides the desired traffic-to-pilot ratio <b>720</b> and RICH-to-pilot ratio <b>730</b> for each particular data rate <b>710</b> at which the mobile terminal <b>105</b> transmits data over the traffic channel R-DPDCH <b>424</b> to the base transceiver site <b>110</b>. As the data rate <b>710</b> of the traffic channel R-DPDCH <b>424</b> increases, the difference between the traffic-to-pilot ratio <b>720</b> and the RICH-to-pilot ratio <b>730</b> increases. It will be appreciated that the specific values of the traffic-to-pilot and RICH-to-pilot ratios <b>720</b>, <b>730</b> for the particular data rates <b>710</b> provided within the table <b>700</b> are merely exemplary. Accordingly, the values of the traffic-to-pilot and RICH-to-pilot ratios <b>720</b>, <b>730</b> need not necessarily be limited to the examples shown, but may include other values without departing from the spirit and scope of the present invention.

0045The RICH-to-pilot ratio <b>730</b> within the table <b>700</b> for a particular data rate <b>710</b> is used by the base transceiver site <b>110</b> to more accurately estimate the SNR of the pilot channel DPCCH <b>422</b> and the traffic channel R-DPDCH <b>424</b>. Specifically, in one embodiment, the estimated SNR of the pilot channel DPCCH <b>422</b> is the product of the measured SNR of the rate indicator channel R-RICH <b>426</b> and the inverse of the RICH-to-pilot ratio <b>730</b> for a particular data rate <b>710</b> over the traffic channel R-DPDCH <b>424</b>. The symbol SNR for the traffic channel R-DPDCH <b>424</b> is the product of the measured SNR of the rate indicator channel R-RICH <b>426</b>, the inverse of the RICH-to-pilot ratio <b>730</b>, and the traffic-to-pilot ratio <b>720</b> for a particular data rate <b>710</b> over the traffic channel R-DPDCH <b>424</b>. The estimated pilot SNR is used by the base transceiver site <b>110</b> to more accurately perform inner-loop power control and the estimated symbol SNR is used for metric scaling in turbo decoding. A more detailed description of how the base transceiver site <b>110</b> determines the pilot SNR and symbol SNR is provided below.

0046To determine the SNR of the pilot channel DPCCH <b>422</b>, the SNR of the rate indicator channel R-RICH <b>426</b> is measured. According to the illustrated embodiment, symbols from the traffic channel R-DPDCH <b>424</b> are stored in the memory <b>325</b> of the base transmitter site <b>110</b> as they are received from the mobile terminal <b>105</b>. The normalized RICH symbol (x_k) from the rate indicator channel R-RICH <b>426</b> that is received after pilot filtering (e.g., channel estimation and de-rotation) may be represented by the following equation.

0047<maths id="MATH-US-00001" num="00001"><math overflow="scroll"><mtable><mtr><mtd><mrow><msub><mi>x</mi><mi>k</mi></msub><mo>=</mo><mi /><mo>⁢</mo><mrow><mrow><msup><mrow><mo></mo><msub><mi>α</mi><mi>k</mi></msub><mo></mo></mrow><mn>2</mn></msup><mo>·</mo><msqrt><mfrac><msub><mi>E</mi><mi>cp</mi></msub><msub><mi>I</mi><mi>o</mi></msub></mfrac></msqrt><mo>·</mo><msqrt><mfrac><mrow><msub><mi>E</mi><mrow><mi>c</mi><mo>,</mo><mi>rich</mi></mrow></msub><mo>·</mo><mi>SF</mi></mrow><msub><mi>I</mi><mi>o</mi></msub></mfrac></msqrt><mo>·</mo><msup><mi>ⅇ</mi><mrow><mi>j</mi><mo>·</mo><mi>ϕ</mi></mrow></msup></mrow><mo>+</mo><mrow><msup><mi>α</mi><mo>*</mo></msup><mo>·</mo><msqrt><mfrac><msub><mi>E</mi><mi>cp</mi></msub><msub><mi>I</mi><mi>o</mi></msub></mfrac></msqrt><mo>·</mo><msqrt><mfrac><msub><mi>N</mi><mi>t</mi></msub><mrow><mn>2</mn><mo>·</mo><msub><mi>I</mi><mi>o</mi></msub></mrow></mfrac></msqrt><mo>·</mo></mrow></mrow></mrow></mtd></mtr><mtr><mtd><mrow><mi /><mo>⁢</mo><mrow><mo>{</mo><mrow><msub><mi>n</mi><mi>kl</mi></msub><mo>+</mo><mrow><mi>j</mi><mo>·</mo><msub><mi>n</mi><mi>kQ</mi></msub></mrow></mrow><mo>}</mo></mrow></mrow></mtd></mtr><mtr><mtd><mrow><msub><mi>p</mi><mi>k</mi></msub><mo>=</mo><mi /><mo>⁢</mo><mrow><mrow><mi>α</mi><mo>·</mo><msqrt><mfrac><mrow><msub><mi>E</mi><mi>cp</mi></msub><mo>·</mo><msub><mi>SF</mi><mi>p</mi></msub></mrow><msub><mi>I</mi><mi>o</mi></msub></mfrac></msqrt><mo>·</mo><msup><mi>ⅇ</mi><mrow><mi>j</mi><mo>·</mo><mi>ϕ</mi></mrow></msup></mrow><mo>+</mo><mrow><msqrt><mfrac><msub><mi>N</mi><mi>t</mi></msub><mrow><mn>2</mn><mo>·</mo><msub><mi>I</mi><mi>o</mi></msub></mrow></mfrac></msqrt><mo>·</mo><mrow><mo>{</mo><mrow><msub><mi>u</mi><mi>kl</mi></msub><mo>+</mo><mrow><mi>j</mi><mo>·</mo><msub><mi>u</mi><mi>kQ</mi></msub></mrow></mrow><mo>}</mo></mrow></mrow></mrow></mrow></mtd></mtr></mtable></math></maths><br /> wherein α_k=Fading coefficient <ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0000"><ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0048">E_c,rich=Energy per RICH chip</li><li id="ul0002-0002" num="0049">E_cp=Energy per Pilot chip</li><li id="ul0002-0003" num="0050">SF=Spread Factor of RICH</li><li id="ul0002-0004" num="0051">SF_p=Spread Factor of Pilot</li><li id="ul0002-0005" num="0052">I_o=Total Received power spectral density</li><li id="ul0002-0006" num="0053">φ=Phase</li><li id="ul0002-0007" num="0054">N_t=Noise plus Interference power spectral density <br /> n_k1, n_kQ, u_k1, u_kQ=Complex noise plus interference terms </li></ul></li></ul>

0055The SNR of the rate indicator channel R-RICH <b>426</b> may be determined by either accumulating the RICH symbols non-coherently, coherently, or a combination of coherent and non-coherent accumulation. When accumulating the RICH symbols non-coherently, each RICH symbol's energy is summed across the RICH transmission. An example of non-coherent accumulation may be represented by the following equation, which provides an estimate of the RICH symbol energy (E_s,rich/I_o).

0056<maths id="MATH-US-00002" num="00002"><math overflow="scroll"><mrow><mfrac><msub><mi>E</mi><mrow><mi>s</mi><mo>,</mo><mi>rich</mi></mrow></msub><msub><mi>I</mi><mi>o</mi></msub></mfrac><mo>=</mo><mrow><mfrac><mn>1</mn><mi>N</mi></mfrac><mo>·</mo><mrow><munderover><mo>∑</mo><mrow><mi>k</mi><mo>=</mo><mn>0</mn></mrow><mrow><mi>N</mi><mo>-</mo><mn>1</mn></mrow></munderover><mo>⁢</mo><mstyle><mspace width="0.3em" height="0.3ex" /></mstyle><mo>⁢</mo><msup><mrow><mo></mo><msub><mi>x</mi><mi>k</mi></msub><mo></mo></mrow><mn>2</mn></msup></mrow></mrow></mrow></math></maths><br /> An estimate of the noise power spectral density (N_t/I_o) is represented by the following equation.

0057<maths id="MATH-US-00003" num="00003"><math overflow="scroll"><mrow><mfrac><msub><mi>N</mi><mi>t</mi></msub><msub><mi>I</mi><mi>o</mi></msub></mfrac><mo>=</mo><mrow><mfrac><mn>1</mn><mrow><mi>N</mi><mo>-</mo><mn>1</mn></mrow></mfrac><mo>·</mo><mrow><munderover><mo>∑</mo><mrow><mi>k</mi><mo>=</mo><mn>0</mn></mrow><mrow><mi>N</mi><mo>-</mo><mn>2</mn></mrow></munderover><mo>⁢</mo><mstyle><mspace width="0.3em" height="0.3ex" /></mstyle><mo>⁢</mo><msup><mrow><mo></mo><mrow><msub><mi>p</mi><mrow><mi>k</mi><mo>+</mo><mn>1</mn></mrow></msub><mo>-</mo><msub><mi>p</mi><mi>k</mi></msub></mrow><mo></mo></mrow><mn>2</mn></msup></mrow></mrow></mrow></math></maths>

0058When accumulating the RICH symbols coherently, the base transceiver site <b>110</b> decodes the RICH first. If the RICH symbols are repeated across the transmission, the RICH may be decoded after each transmission. Once the decoding is successfully completed, the base transceiver site <b>110</b> knows the transmitted RICH symbols and may then coherently sum the received symbols. An example of coherent accumulation may be represented by the following equation, which provides an estimate of the RICH symbol energy (E_s,rich/I_o)

0059<maths id="MATH-US-00004" num="00004"><math overflow="scroll"><mrow><mfrac><msub><mi>E</mi><mrow><mi>s</mi><mo>,</mo><mi>rich</mi></mrow></msub><msub><mi>I</mi><mi>o</mi></msub></mfrac><mo>=</mo><msup><mrow><mo></mo><mi>y</mi><mo></mo></mrow><mn>2</mn></msup></mrow></math></maths><br /> where:

0060<maths id="MATH-US-00005" num="00005"><math overflow="scroll"><mrow><mi>y</mi><mo>=</mo><mrow><mfrac><mn>1</mn><mi>N</mi></mfrac><mo>·</mo><mrow><munderover><mo>∑</mo><mrow><mi>k</mi><mo>=</mo><mn>0</mn></mrow><mrow><mi>N</mi><mo>-</mo><mn>1</mn></mrow></munderover><mo>⁢</mo><mstyle><mspace width="0.3em" height="0.3ex" /></mstyle><mo>⁢</mo><mrow><msub><mi>x</mi><mi>k</mi></msub><mo>·</mo><msub><mi>z</mi><mi>k</mi></msub></mrow></mrow></mrow></mrow></math></maths><br />z_k=Estimated RICH symbol at time k

0000An estimate of the noise power spectral density (N_t/I_o) may be represented by the following equation.

0061<maths id="MATH-US-00006" num="00006"><math overflow="scroll"><mrow><mfrac><msub><mi>N</mi><mi>t</mi></msub><msub><mi>I</mi><mi>o</mi></msub></mfrac><mo>=</mo><mrow><mfrac><mn>1</mn><mrow><mi>N</mi><mo>-</mo><mn>1</mn></mrow></mfrac><mo>·</mo><mrow><munderover><mo>∑</mo><mrow><mi>k</mi><mo>=</mo><mn>0</mn></mrow><mrow><mi>N</mi><mo>-</mo><mn>2</mn></mrow></munderover><mo>⁢</mo><mstyle><mspace width="0.3em" height="0.3ex" /></mstyle><mo>⁢</mo><msup><mrow><mo></mo><mrow><mrow><msub><mi>z</mi><mrow><mi>k</mi><mo>+</mo><mn>1</mn></mrow></msub><mo>·</mo><msub><mi>x</mi><mrow><mi>k</mi><mo>+</mo><mn>1</mn></mrow></msub></mrow><mo>-</mo><mrow><msub><mi>z</mi><mi>k</mi></msub><mo>·</mo><msub><mi>x</mi><mi>k</mi></msub></mrow></mrow><mo></mo></mrow><mn>2</mn></msup></mrow></mrow></mrow></math></maths><br /> For non-coherent and coherent accumulations, the SNR (E_s,rich/N_t) of the rate indicator channel R-RICH <b>426</b> may then be derived by the following equation.

0062<maths id="MATH-US-00007" num="00007"><math overflow="scroll"><mrow><mfrac><msub><mi>E</mi><mrow><mi>s</mi><mo>,</mo><mi>rich</mi></mrow></msub><msub><mi>N</mi><mi>t</mi></msub></mfrac><mo>=</mo><mrow><mfrac><msub><mi>E</mi><mrow><mi>s</mi><mo>,</mo><mi>rich</mi></mrow></msub><msub><mi>I</mi><mi>o</mi></msub></mfrac><mo>·</mo><mfrac><msub><mi>I</mi><mi>o</mi></msub><msub><mi>N</mi><mi>t</mi></msub></mfrac></mrow></mrow></math></maths>

0063Once the SNR (E_s,rich/N_t) of the rate indicator channel R-RICH <b>426</b> is obtained, the SNR (E_c,pilot/N_t) of the pilot channel DPCCH <b>422</b> may be obtained from the equation below.

0064<maths id="MATH-US-00008" num="00008"><math overflow="scroll"><mrow><mfrac><msub><mi>E</mi><mrow><mi>c</mi><mo>,</mo><mi>pilot</mi></mrow></msub><msub><mi>N</mi><mi>t</mi></msub></mfrac><mo>=</mo><mrow><mfrac><msub><mi>E</mi><mrow><mi>s</mi><mo>,</mo><mi>rich</mi></mrow></msub><msub><mi>N</mi><mi>t</mi></msub></mfrac><mo>·</mo><mfrac><msub><mi>E</mi><mrow><mi>c</mi><mo>,</mo><mi>pilot</mi></mrow></msub><msub><mi>E</mi><mrow><mi>c</mi><mo>,</mo><mi>rich</mi></mrow></msub></mfrac></mrow></mrow></math></maths><br /> In particular, the SNR (E_c,pilot/N_t) of the pilot channel DPCCH <b>422</b> is determined by taking the product of the measured SNR (E_s,rich/N_t) of the rate indicator channel R-RICH <b>426</b> (as obtained above) and the inverse of the RICH-to-pilot ratio <b>730</b> for a particular data rate over the traffic channel R-DPDCH <b>424</b> from the table <b>700</b> stored within memory <b>325</b> of the base transceiver site <b>110</b>. As mentioned, the RICH-to-pilot ratio <b>730</b> is the energy-per-chip ratio between the rate indicator signal and the pilot signal (E_c,rich/E_c,pilot). Once the SNR (E_c,pilot/N_t) of the pilot channel DPCCH <b>422</b> is obtained, the pilot SNR may be used to more accurately perform inner-loop power control by the base transceiver site <b>110</b> for communicating with the mobile terminal <b>105</b>. The manner in which the base transceiver site <b>110</b> performs inner-loop power control based on an estimated pilot SNR is well known to those of ordinary skill in the art. Accordingly, the details for determining such power control based on the pilot SNR will not be disclosed herein to avoid unnecessarily obscuring the present invention.

0065The symbol SNR (E_s,data/N_t) for metric scaling may be derived by the following equation.

0066<maths id="MATH-US-00009" num="00009"><math overflow="scroll"><mrow><mfrac><msub><mi>E</mi><mrow><mi>s</mi><mo>,</mo><mi>data</mi></mrow></msub><msub><mi>N</mi><mi>t</mi></msub></mfrac><mo>=</mo><mrow><mfrac><msub><mi>E</mi><mrow><mi>s</mi><mo>,</mo><mi>rich</mi></mrow></msub><msub><mi>N</mi><mi>t</mi></msub></mfrac><mo>·</mo><mfrac><msub><mi>E</mi><mrow><mi>c</mi><mo>,</mo><mi>data</mi></mrow></msub><msub><mi>E</mi><mrow><mi>c</mi><mo>,</mo><mi>pilot</mi></mrow></msub></mfrac><mo>·</mo><mfrac><msub><mi>E</mi><mrow><mi>c</mi><mo>,</mo><mi>pilot</mi></mrow></msub><msub><mi>E</mi><mrow><mi>c</mi><mo>,</mo><mi>rich</mi></mrow></msub></mfrac></mrow></mrow></math></maths><br /> The symbol SNR (E_s,data/N_t) is determined by taking the product of the measured SNR (E_s,rich/N_t) of the rate indicator channel R-RICH <b>426</b>, the inverse of the RICH-to-pilot ratio <b>730</b>, and the traffic-to-pilot ratio <b>720</b> for a particular data rate over the traffic channel R-DPDCH <b>424</b>. As previously mentioned, the RICH-to-pilot ratio <b>730</b> and traffic-to-pilot ratio <b>720</b> for a particular data rate <b>710</b> on the traffic channel R-DPDCH <b>424</b> are obtained from the table <b>700</b> stored within the memory <b>325</b> of the base transceiver site <b>110</b>. The estimated symbol SNR (E_s,data/N_t) is then used by the base transceiver site <b>110</b> for metric scaling in turbo decoding. The manner in which the base transceiver site <b>110</b> performs metric scaling based on an estimated symbol SNR is well known to those of ordinary skill in the art. Accordingly, the details for determining such metric scaling based on the symbol SNR will not be disclosed herein to avoid unnecessarily obscuring the present invention.

0067Turning now to <figref idref="DRAWINGS">FIG. 8</figref>, a method for providing an estimation of a pilot SNR and symbol SNR is shown in accordance with one embodiment of the present invention. At block <b>810</b>, the receiver <b>310</b> of the base transceiver site <b>110</b> receives the pilot, data, and rate indicator signals over the respective pilot channel DPCCH <b>422</b>, traffic channel R-DPDCH <b>424</b>, and rate indicator channel R-RICH <b>426</b> transmitted from the mobile terminal <b>105</b>. According to one embodiment, the rate indicator channel R-RICH <b>426</b> is transmitted in a code division multiplex (CDM) manner as illustrated in <figref idref="DRAWINGS">FIG. 5A</figref>, in which the rate indicator channel R-RICH <b>426</b> is transmitted on a separate code channel from the traffic channel R-DPDCH <b>424</b>. In an alternative embodiment, the rate indicator channel R-RICH <b>426</b> may be transmitted in a time division multiplex (TDM) manner with the traffic channel R-DPDCH <b>424</b> on the same code channel on a time division basis as illustrated in <figref idref="DRAWINGS">FIG. 5B</figref>.

0068At block <b>820</b>, the base transceiver site <b>110</b> stores symbols from the traffic channel R-DPDCH <b>424</b> as they are received from the mobile terminal <b>105</b>. The processor <b>320</b> of the base transceiver site <b>110</b> estimates the SNR of the rate indicator channel R-RICH <b>426</b> either non-coherently, coherently, or a combination of both coherent and non-coherent accumulation at block <b>830</b>. Specifically, when accumulating the RICH symbols non-coherently, each RICH symbol's energy is summed across the RICH transmission. When accumulating the RICH symbols coherently, the base transceiver site <b>110</b> decodes the RICH first. If the RICH symbols are repeated across the transmission, the RICH may be decoded after each transmission. Once the decoding is successfully completed, the base transceiver site <b>110</b> knows the transmitted RICH symbols and may then coherently sum the received symbols. Examples of non-coherent and coherent accumulation, which provide an estimate of the RICH symbol energy (E_s,rich/I_o) have been previously provided. In one embodiment, the SNR (E_s,rich/N_t) of the rate indicator channel R-RICH <b>426</b> may then be derived by taking the product of the RICH symbol energy (E_s,rich/I_o) and the inverse of the noise power spectral density (N_t/I_o), the equations of which have been also previously provided.

0069At block <b>840</b>, the processor <b>320</b> of the base transceiver site <b>110</b> determines the pilot SNR (E_c,pilot/N_t) of the pilot channel DPCCH <b>422</b> by taking the product of the measured SNR of the rate indicator channel R-RICH <b>426</b> and the inverse of the RICH-to-pilot ratio <b>730</b> for a particular data rate <b>710</b> over the traffic channel R-DPDCH <b>424</b> from the table <b>700</b> stored within memory <b>325</b> of the base transceiver site <b>110</b> as shown by the equation below.

0070<maths id="MATH-US-00010" num="00010"><math overflow="scroll"><mrow><mfrac><msub><mi>E</mi><mrow><mi>c</mi><mo>,</mo><mi>pilot</mi></mrow></msub><msub><mi>N</mi><mi>t</mi></msub></mfrac><mo>=</mo><mrow><mfrac><msub><mi>E</mi><mrow><mi>s</mi><mo>,</mo><mi>rich</mi></mrow></msub><msub><mi>N</mi><mi>t</mi></msub></mfrac><mo>·</mo><mfrac><msub><mi>E</mi><mrow><mi>c</mi><mo>,</mo><mi>pilot</mi></mrow></msub><msub><mi>E</mi><mrow><mi>c</mi><mo>,</mo><mi>rich</mi></mrow></msub></mfrac></mrow></mrow></math></maths><br /> Once the SNR of the pilot channel DPCCH <b>422</b> is obtained, the pilot SNR may be used to perform inner-loop power control by the base transceiver site <b>110</b> for communicating with the mobile terminal <b>105</b> using methods well-established in the art.

0071At block <b>850</b>, the processor <b>320</b> of the base transceiver site <b>110</b> determines the symbol SNR (E_s,data/N_t) of the traffic channel R-DPDCH <b>424</b> by taking the product of the measured SNR of the rate indicator channel R-RICH <b>426</b>, the inverse of the RICH-to-pilot ratio <b>730</b>, and the traffic-to-pilot ratio <b>720</b> for a particular data rate over the traffic channel R-DPDCH <b>424</b> as shown by the equation below.

0072<maths id="MATH-US-00011" num="00011"><math overflow="scroll"><mrow><mfrac><msub><mi>E</mi><mrow><mi>s</mi><mo>,</mo><mi>data</mi></mrow></msub><msub><mi>N</mi><mi>t</mi></msub></mfrac><mo>=</mo><mrow><mfrac><msub><mi>E</mi><mrow><mi>s</mi><mo>,</mo><mi>rich</mi></mrow></msub><msub><mi>N</mi><mi>t</mi></msub></mfrac><mo>·</mo><mfrac><msub><mi>E</mi><mrow><mi>c</mi><mo>,</mo><mi>data</mi></mrow></msub><msub><mi>E</mi><mrow><mi>c</mi><mo>,</mo><mi>pilot</mi></mrow></msub></mfrac><mo>·</mo><mfrac><msub><mi>E</mi><mrow><mi>c</mi><mo>,</mo><mi>pilot</mi></mrow></msub><msub><mi>E</mi><mrow><mi>c</mi><mo>,</mo><mi>rich</mi></mrow></msub></mfrac></mrow></mrow></math></maths><br /> As previously mentioned, the RICH-to-pilot ratio <b>730</b> and traffic-to-pilot ratio <b>720</b> for a particular data rate <b>710</b> on the traffic channel R-DPDCH <b>424</b> are obtained from the table <b>700</b> stored within the memory <b>325</b> of the base transceiver site <b>110</b>. The estimated symbol SNR may then be used by the base transceiver site <b>110</b> for metric scaling in turbo decoding using methods well established in the art.

0073By keeping the signal power level of the pilot channel DPCCH <b>422</b> to a nominal signal power level to accommodate higher data rates over the traffic channel R-DPDCH <b>424</b> may cause the estimation of the SNR of the pilot channel DPCCH <b>422</b> to not be as precise as if it were transmitted at a higher signal power level. By measuring the SNR of the rate indicator channel R-RICH <b>426</b>, which is transmitted at a higher signal power level than the pilot channel R-DPCCH <b>422</b>, a more accurate estimation of the pilot channel SNR may be determined using the methods described above. As a result of achieving a more accurate SNR of the pilot channel DPCCH <b>422</b>, the wireless communication system <b>100</b> may achieve a more efficient inner-loop power control and symbol scaling for turbo decoding.

0074Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

0075Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

0076The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

0077The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

0078The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.